Creating and maintaining ship channels, ports, and other man-made waterway formations requires the removal of material from the bottom of navigable water ways. Frequently, the material is dredged from the water way and disposed in a dredged material placement area (commonly referred to as a placement area), which typically consists of an enclosed levee structure on land relatively near the dredge site, so that the material may be readily transported from the dredge site to the placement area. The material disposed of in a placement area may comprise a mixture of solids and liquids, and typically dry out after its disposal in the placement area. Accordingly, the upper surface of material in a placement area may comprise a solid “crust” layer, while deeper material may have a semi-solid consistency. Because of persistent shoaling, most navigable water ways require continuous dredging to maintain the depth and width of a navigable water way through ongoing dredging operations. In many cases, the areas around dredge sites are occupied by industrial, commercial or residential areas and there is limited space for placement areas. Additionally, as placement areas become filled with dredge material, placement area owners begin a continuous cycle of furrowing ditches into the contained dredge material to create surface area and dry the material, thereby compacting it to gain capacity. Eventually, levees must be raised at the risk of levee instability and ultimate failure, chancing a material breach. Therefore, it may be advantageous to reuse placement areas by removing the material completely so they can be filled with dredged material again.
Excavating placement areas has been proposed in the past as a method for allowing their reuse. Previous attempts have included operations such as using an excavator or backhoe to “mechanically” dredge material from the placement area. The material is loaded onto a truck or barge and moved to a beneficial use or secondary disposal site. The secondary disposal site may be a landfill or an EPA-designated offshore site. This method presents several shortcomings. First, because the material in the placement area must be sufficiently dry before it can be excavated using traditional earth moving equipment, this method requires leaving the placement area unused for a long period of time (typically years) after it is filled. This process may be considered a drying cycle. This results in downtime during which the placement area cannot be used. Second, this method merely moves material from one disposal area to another, which is very inefficient. Third, if amphibious “marsh buggie” excavation equipment was to be used to remove the material, negating the need for long drying time, removal would take a very long time and would be very uneconomical. Lastly, to create more capacity in existing placement areas, levee raises may occur and essentially increase the available volume of the placement area. However, this is not sustainable because there are limits to how tall these levees can be built before they fail under their own weight or become too costly to build. Creating a new placement area is rare because of federal permitting constraints and is also a costly endeavor due to the non-availability of real estate along ship channels, especially in industrialized areas. Therefore, these traditional methods may experience potential losses in the form of placement area downtime, costly and inefficient use of secondary disposal areas, or uneconomical means of dredged material removal.